Suspensions are available in the prior art which utilize air springs to provide an extremely comfortable ride, even for large over-the-road type trucks and other heavy vehicles. However, one drawback of an air spring type suspension is that the mushiness of the air spring requires increased stabilization of the axle with respect to the chassis. Otherwise, the axle would have a tendency to overreact to inconsistencies in the road surface, causing an unsafe and unstable ride. Also, with an unstabilized axle and air spring suspension the relative distribution of the load over the bed of the truck would significantly affect the ride and driving characteristics, greatly reducing the versatility of the vehicle and requiring an inordinate amount of attention to placement of the load. Indeed, proper placement of some types of unbalanced loads might be impossible under some circumstances to ensure a stable and safe ride.
Applicant has previously invented and patented several air spring type suspensions which include parallelogram stabilization of the axle. The parallelogram type of axle stabilization has been found to be a significant advancement over the prior art. With applicant's patented air spring suspension on systems using parallelogram stabilization, a safe, stable, and comfortable ride for all types of loads has been achieved. Some of these suspensions are described in U.S. Pat. Nos. 4,114,923 and 4,132,432, the disclosures of which are incorporated herein by reference.
Another problem with air spring type suspensions is that they are particularly susceptible to oscillation of the axle about the longitudinal axis of the truck, i.e., from side to side. This is more of a problem in air spring suspensions because the air spring does not offer any resistance to longitudinal oscillation such as a leaf spring or other type of solid spring. To solve the problem of controlling the oscillation of the axle about the longitudinal axis of the truck, applicant has previously invented and patented a suspension which provides resilient bushings between a bolster beam and a torque beam, the axle being rigidly mounted to the booster beam. A fixed axle mount stabilizes the axle with respect to the suspension and is used instead of a parallelogram stabilized axle. In this suspension, longitudinal oscillation is controlled by the resilient members of the bushings so that flexing or oscillation of the bolster beam and axle assembly with respect to the torque beam is limited. This suspension is described in U.S. Pat. No. 3,801,086, the disclosure of which is incorporated herein by reference. Applicant's patented suspension providing resistance to longitudinal oscillation with a fixed axle mount is a good and useful invention which has also met with wide success in the industry.
Both types of air spring suspensions previously invented and patented by applicant offer features which were unavailable in the prior art. Applicant has now succeeded in combining the advantages of both of the suspensions by inventing an air spring type suspension which has parallelogram stabilizing of a pivotally mounted axle and also controls oscillation of the axle about the longitudinal axis of the truck. The suspension includes a first torque beam rigidly pivotally connected to a hanger assembly at one end with a pair of resilient bushings connecting it to a second beam. The axle is rigidly pivotally mounted to the second beam and an air spring extends between the second beam and the chassis. Thus, a solid pivotal connection is made between the axle and the second beam and all the longitudinal oscillation induced between the chassis and the suspension assembly is absorbed and controlled by the two resilient bushings connecting the first torque beam to the second beam. The spaced apart pair of bushings with resilient members provide a stable base to aid in controlling longitudinal oscillation of the chassis and provide much greater control than if a single resilient bushing were used.
The parallelogram is formed by the hanger assembly, the combination of the first and second torque beam, the axle seat and axle housing, and an upper torque rod which extends between the rear axle housing and a transverse chassis member. The upper torque arm and the first and second beam combination both form a lever which is pivotally attached to the chassis with the axle mounted therebetween so that upward or downward movement of the axle with respect to the chassis is controlled by these two levers. This controlled movement ensures that the pitch of the axle with respect to vertical remains virtually constant independently of the type of load or terrain.
The parallelogram action of the suspension is made possible through the rigid pivotal mounting of the axle to the second beam. This rigid pivotal mounting of the axle permits the axle to freely pivot in the fore and aft direction as it deflects vertically with respect to the chassis. However, longitudinal oscillatory forces have no effect on this rigid pivotal connection and instead are absorbed in the two resilient bushings connecting the first and second torque beams. Similarly, the first and second torque beams are fixedly attached to each other as they are joined a two points along their lengths. Therefore there is no allowable pivotal action between these two torque beams such as would interfere with the parallelogram stabilization of the axle. Through this scheme, applicant has combined the advantages of two separate suspensions in such a way that they are independent of one another and do not detract from either's function.
Thus, applicant's invention provides the advantages of an air-spring member for comfort and smoothness of ride, a parallelogram controlled axle which maintains the pitch of the axle virtually constant as the axle deflects vertically with respect to the chassis, and controlled oscillation of the axle about the longitudinal axis of the chassis, the oscillation control being accomplished by two resilient bushings being spaced apart to provide a base of stabilization to increase its effectiveness.
Applicant's new suspension system and some of the advantages thereof have been briefly described above. A more detailed description and explanation follows in the drawings and the description of the preferred embodiment.